Residential and small commercial foundations constructed in modern times are generally a concrete slab having a small beam about the periphery and spaced intermittently between the sides of the slab to support the house. As long as upper soil conditions remain stable, the slab provides adequate support for the use intended. However, variations in the moisture content of the supporting sub soil caused by excessive watering of the flower beds adjacent the foundation, poor drainage away from the foundation, leaking plumbing, non-uniform watering of flowers, shrubs or the lawn around the house, or any concentration of water at one or more points around the foundation or extremes in climatic conditions (dry summer, wet winter) cause expansive soils such as clay to either exert a pressure upwardly on the foundation or dry and lose strength thus causing the slab to crack and and become unlevel.
Once the foundation is cracked, it becomes unlevel and causes cracks in the masonry and interior walls of the house which are unattractive and allow needless escape of heated or cooled air from the home.
Although not as suspectible if properly constructed pier and beam foundations are also subject to moving and becoming unlevel if the piers do not extend to bed rock.
Heretofore, attempts to correct the levelling problem have been achieved by two methods. The first method is commonly called mud-jacking wherein a soil cement grout is pumped beneath the slab, under pressure, to produce a lifting force which literally floats the slab to the desired position. Introduction of the grout through small holes in the slab allows lifting of a portion of the slab.
A second method, which is often combined with mud-jacking is mechanically raising of the slab and back filling with the soil cement grout. The mechanical method represents a certain improvement over the pressure injection however, it is generally limited to the perimeter of the beam due to accessibility of equipment.
Heretofore, drilling holes about the perimeter of the beam to allow mechanical lifting of slab has been achieved by placing the drill as close to the foundation as possible and drilling under the foundation. Because of the equipment heretofore devised, the drill generally projects under the beam at a 30 to 45 degree angle. This is undesirable in that only the vertical components directly under the beam provide support for the foundation.
It has been found that in order to properly correct the problem of a settling foundation one must drill below the unstabilized soil. Soil becomes stable at a distance of only 7 to 8 feet below the ground and is generally unstable above that heighth and therefore it is necessary to drill 7 to 8 feet below the foundation level in order to provide proper support to prevent further collapsing of the foundation. This distance may vary depending upon the type of soil in the area, however, this figure is generally true for clay type soils found in black lands.